1. Field of the Invention
This invention relates to a method for obtaining wheel alignment in a vehicle having steerable front wheels and nonsteerable rear wheels and more particularly to such a method wherein the reference for the steerable wheel alignment is provided by the orientation of the nonsteerable wheels.
2. Description of the Prior Art
One manner in which the toe of the front steerable wheels on a vehicle is measured is disclosed in U.S. Pat. No. 4,097,157, Lill, issued June 27, 1978. The individual toe of one of the front wheels is measured with respect to the axis of rotation of the rear wheel on the same side of the vehicle. The total toe is then measured between the two front steerable wheels. By subtracting the toe of the front wheel measured with respect to the axis of the rear wheel from the total front wheel toe, the individual toe of the second of the two front steerable wheels is found.
An apparatus is disclosed in U.S. Pat. No. 3,091,862, MacMillan, issued June 4, 1963, in which a pair of right and left hand targets are positioned in known relationship with the rear wheels on a vehicle. Sighting tubes are provided which are aligned with the planes parallel to the steerable front wheel planes and which are directed rearwardly toward the targets on each side of the vehicle. The steering angle of the front wheels is adjusted until similar points on the rear positioned targets are observed through the sight tubes. The wheels are now steered straight ahead relative to the rear wheels and the steering wheel inside the car may be adjusted to a centered position by well known mechanical adjustments.
U.S. Pat. No. 2,972,189, Holub, issued Feb. 21, 1961 relates to apparatus for checking wheel alignment of automobiles which includes telescopes mounted on each of the front steerable wheels together with a third telescope mounted midway bwtween the two front wheels. The third telescope is utilized to sight along predetermined center points on the frame of the vehicle. The function of the third telescope is to check the alignment of the frame as well as the relation of the frame with the front end and rear housing. The telescopes mounted on the steerable wheels may be trained at specified points on the rear wheels. If scales associated with the direction of train of the telescopes in a horizontal plane read substantially the same, the tracking of the front wheels with the rear wheels is presumably satisfactory. The centrally mounted telescope is used to verify vehicle frame alignment.
U.S. Pat. No. 3,855,709, Hirmann, issued Dec. 24, 1974 discloses a system which includes an electromechanical computer which ascertains the centerline of a vehicle and makes wheel alignment measurements relative to the centerline. The apparatus disclosed by Hirmann is fixed in position surrounding a space into which a vehicle is driven. The alignment characteristics of the vehicle wheels are thereafter measured by the apparatus fixed in position and surrounding the vehicle.
An optical system is disclosed in U.S. Pat. No. 4,058,903, Wilkerson, issued Nov. 22, 1977, in which sighting tubes and scales are provided at both the front and the rear of the vehicle. The sighting tubes and scales are mounted on structure which is positioned adjacent to the vehicle. The scales are sighted through the tubes so that information relating to the angular orientation of each wheel pair axis relative to a vehicle steering axis is obtained. The stated purpose of the apparatus is to ascertain certain faults in the alignment of the vehicle frame and not to align the wheels of the vehicle.